I fish the north fork a lot. Though this year I haven't hit it as much because of the conditions and lack of fish.
Harassment of the kings isn't limited to one type of person and not all of them are trying to snag. It ranges from guys who think those big fish they see are steelhead, to people who know better but are desperate for a tug at the end of the day, to tarheels who are only using a fly rod to make their snagging draw less attention.

"But why would WDFW take such action if fly fishers weren't snagging these fish?"
Because targeting kings on the north fork is illegal. Trying to hook one in the mouth is just as illegal as trying to hook one in the ass.

"And one more question, does using a weighted line that sinks qualify as using a weighted fly? If not why?"
No it doesn't. I'm not sure why. I suppose the state could have made it so that we can only use floating lines. Most people fish floaters anyway when it gets low.

For someone who admittedly doesn't know the river, you imply a lot about the people who fish it.